Disorders of the neuromuscular junction and muscle

Question 1

What are motor end plates?

Answer 1

Synapses which form between motor neurones and the muscle

Question 2

Describe the locations of endomysium, perimysium and epimysium

Answer 2

Endomysium surrounds muscle fibres

Perimysium surrounds fascicles

Epimysium surrounds individual muscles

Question 3

Describe the different muscle fibre types

Answer 3

Type I - slow oxidative, faitgue resistant

Type IIa - fast oxidative, aerobic metabolism

Type IIb - fast glycolytic, easily fatigues

Question 4

Give examples of presynaptic disorders

Answer 4

Botulism

Lambert eaton myasthenic syndrome (LEMS)

Question 5

Which organism causes botulism and where is it found?

Answer 5

Clostridium botulinum

Organism present in soil which can infect food and wounds

IVDU can become infected if their drugs are not clean

Question 6

How does botulism present?

Answer 6

Neuromuscular and respiratory weakness

Question 7

What is lambert eaton myasthenia syndrome?

Answer 7

A paraneoplastic syndrome with antibodies to presynaptic calcium channels

Question 8

How does lambert eaton myasthenia syndrome present?

Answer 8

Affects large muscles - patient struggles to get up

Symptoms improve with exercise

Question 9

Lambert eaton myasthenia syndrome is strongly associated with which condition?

Answer 9

Small cell carcinoma

Question 10

How is lambert eaton myasthenia syndrome treated?

Answer 10

3-4 diaminopyridine

Question 11

Give an example of a postsynaptic disorder

Answer 11

Myaesthenia Gravis

Question 12

Which antibodies are involved in myasthenia gravis?

Answer 12

Anti AChR

Anti Musk

Question 13

What is the most common disorder of the neuromuscular junction?

Answer 13

Myasthenia Gravis

Question 14

Who gets myasthenia graves?

Answer 14

More common in females

Presents in females in the 3rd decade

Presents in males in the 6th or 7th decade

Question 15

What is the pathophysiology behind myasthenia gravis?

Answer 15

Reduced numbers of functioning (ACh) receptors leads to muscle weakness and fatigueabillity

Flattening of endplate folds

75% of patients also have hyperplasia of the thymus

Question 16

Describe the clinical presentation of myasthenia gravis

Answer 16

Fluctuating weakness

Diplopia and bilateral ptosis (EO muscle weakness)

Tired chewing meals (facial and bulbar muscle weakness)

Proximal limb weakness

Respiratory muscle weakness (late presentation)

Question 17

How can myasthenia graves be treated acutely and chronically?

Answer 17

ACUTE TREATMENT
Acetylcholinesterase inhibitors
IV immunoglobulin
Thymectomy

CHRONIC TREATMENT
High dose steroids and steroid sparing agents
Plasma exchange or immunoglobulin

Question 18

Which medication needs to be avoided in patients with myasthenia gravis due to the risk of myasthenia crisis?

Answer 18

Gentamicin

Question 19

What are fasciculations and what causes them?

Answer 19

Fast spontaneous twitches in muscle

May occur in healthy muscle and be precipitated by stress, caffeine and fatigue

May occur in denervated muscle which has become hyper excitable

Question 20

What is myotonia?

Answer 20

Failure of muscle relaxation after use

Question 21

What is myalgia?

Answer 21

Muscle weakness, wasting and hyporeflexia

Question 22

What causes rhabdomyolysis?

Answer 22

Extreme exercise

Falls

Crush injuries

Acute renal failure and DIC

Question 23

What is rhabdomyolysis?

Answer 23

Damage to skeletal muscle causes leakage of toxic intracellular contents into plasma

Question 24

What triad of symptoms does rhabdomyolysis present with?

Answer 24

Myalgia, muscle weakness and myoglobinuria

Question 25

Give examples of immune mediated muscle disorders

Answer 25

Polymyositis Dermatomyositis

Question 26

Describe polymyositis

Answer 26

Symmetrical proximal muscle weakness develops over weeks to months Raised CK Responds to steroids

Question 27

Describe dermatomyositis

Answer 27

Clinically similar to polymyositis but with skin lesions Helioptrope rash on the face Big association with underlying malignancy

Question 28

What is inclusion body myositis?

Answer 28

A degeneratie muscle disorder Slowly progressive weakness Characteristic sparing of the thumb Occurs age >60

Question 29

Give examples of inherited muscular disorder

Answer 29

Duchenne and Beker muscular dystrophies Myotonic dystrophy

Question 30

Describe the genetics of myotonic dystrophy

Answer 30

Most common of the muscular dystrophies Autosomal dominant inherited disorder Trinucleotide disorder with anticipation

Question 31

Describe how myotonic dystrophy presents

Answer 31

Multisytem Weakness Cataracts and ptosis Frontal balding Cardiac defects

Question 32

What drugs can cause myopathy?

Answer 32

Corticosteroids Statins Amiodarone Diuretics Oral contraceptive